1. Field of the Invention
This invention relates to recording apparatus in which a recording signal such as a video signal or the like is frequency-modulated and then recorded on a recording medium and in particular to a recording disc on which said recording is made.
2. Description of the Prior Art
A prior art video disc recording apparatus will be described first.
FIG. 1 is a systematic block diagram thereof, in which reference numeral 1 denotes a video signal generator, 2 a frequency modulator to receive an output video signal V.sub.in supplied from the video signal generator 1, 3 denotes an optical or photo modulator and 4 denotes an argon Ar laser source. The light beam emitted from the argon laser source 4 is turned on and off by the photo modulator 3 in response to the signal-modulated (FM) frequency derived from the frequency modulator 2. Numeral 5 denotes a color lock composite synchronizing signal generator supplied with the video signal V.sub.in from the video signal generator 1 to generate a color lock composite synchronizing signal. Numeral 6 denotes a rotary servo, 7 denotes a motor, and numeral 8 denotes a recording disc. The rotary servo 6 is supplied with the output from the color lock composite synchronizing signal generator 5 so as to rotate the motor 7 at, for example, 1800 r.p.m in synchronism with the frame of the video signal.
In the conventional video disc recording apparatus, the frequency modulator 2 and the color lock composite synchronizing signal generator 5 are provided dependently and therefore they have no relation between them. The dotted line in FIG. 1, which seems to connect both together is added to clarify the characteristics of the present invention as will be described later.
Numeral 9 designates an optical system feeding base, 10 denotes a feeding motor 11 is a guide shaft for the optical system feeding base 9, and 12 designates a feeding servo for the feeding motor 10. The feeding motor 10 is controlled by the feeding servo 12 so as to align the track pitch on the video disc 8, whereby the optical system feeding base 9 is forwarded at a predetermined feeding pitch (for example, 1.6 .mu.m).
The light beam derived from the argon laser source 4 and turned on and off by the photo modulator 3 is spread by an concave lens 13 provided within the optical system feeding base 9. The optical path (optical axis) of the beam is changed by 90.degree. by a half mirror 14 and passed through a recording lens 15 to focus on the recording disc 8, whereby pits or dots (refer to FIG. 2) are formed on its recording surface 8a. A light beam derived from a helium He -neon laser 16 provided on the optical system feeding base 9 is passed through a beam splitter 17 and spread apart by a concave lens 18. The optical axis thereof is changed by 90.degree. by a half mirror 19 and impinged through the recording lens 15 on the recording disc 8 to be reflected therefrom. The reflected beam is again passed through the recording lens 15, and its optical axis is changed by 90.degree. by the half mirror 19 and passed through the concave lens 18. The optical axis thereof is changed by 90.degree. by the beam splitter 17 and detected by an optical or photo detector 20. The output of the photo detector 20 is applied as a servo signal to a focus servo 21, the output of which is supplied to an actuator 22 so as to control the position of the recording lens 15 such that the light beam emitted from the argon laser source 4 focuses on the recording disc 8.
FIG. 2 is an enlarged diagram showing the arrangement state of pits or dots 24 formed on the recording surface 8a of the recording disc 8 as set forth above. Although in the previously proposed technique, in order to record the video signal of one frame on a track T of one circle form on the recording surface 8a of the recording disc 8, the rotation of the motor 7 is controlled, the FM frequency per se corresponding to the momentary value of the video signal level is not accurately synchronized in phase with each other at every frame so that the pits 24 in adjacent tracks, are not formed in an aligned state as, for example, tracks T.sub.i and T.sub.i+1 (where i is a positive integer) as shown in FIG. 2. Thus in the reproducing mode, depending upon the size of the diameter of the reproducing light beam, crosstalk and jitter are caused making it difficult to increase the recording density and it is necessary to compensate for the jitter.